You could also contact the publisher, explain the situation, and see if you can buy the sheets...
I agree with this. I have contacted publishers three or four times about missing parts (not publishers fault), and have always received replacements. Once the publisher (Z-Man, before Asmodee bought them)didn't even charge me even though it was not their problem.
I can also verify that plexiglass works quite well. In fact, using wet erase markers on the plexiglass keeps one from accidentally erasing what you've written on it.